This invention relates to a glass cover plate for a flat display panel, the cover plate being substantially rectangular in outline and having an outwardly protruded central portion.
A display tube is for displaying a luminous display that may be a numeral, a letter, a symbol, and/or the like. A considerable number of the display tubes are made in a form of a flat display panel comprising a rectangular planar substrate of an electrically insulating material, such as glass or ceramics, and a glass cover plate substantially congruent in outline with the substrate. As will later be described more in detail, the substrate has a plurality of electrodes formed thereon or otherwise attached thereto. The cover plate comprises an outwardly protruded central portion for covering the electrodes and a peripheral flange having a substantially planar surface at which the cover plate is sealed to the substrate.
As will also be described in the following with reference to some of the accompanying drawings, a conventional glass cover plate of the type described has been defective in that the outline thereof deforms during manufacture or embossing of the central portion. Although it is possible to avoid the deformation, either complicated processes of manufacture have been indispensable or the cover plates have been deformed in other respects. In either event, the deformation has been harmful to the flat display panels.